Application of X-ray microanalysis to study the distribution of organic waste in soil

X-ray microanalysis was used to determine the localisation and the distribution of sewage sludge when mixed with a calcareous soil at high doses. The first part of this study was aimed at optimising this technique in order to accurately detect the sludge present in soil. Phosphorus was used as a marker of sludge because this element has shown itself to be the one that best defined the distribution of sludge in soil. The microscope was set up to maximize detection of the phosphorus signal. Thin sections of soil were analysed by X-ray mapping and a semi-quantitative analysis was carried out in order to measure the sludge localization into soil. In the second part of the study, X-ray mapping was used to determine the exact distribution of sewage sludge in soil fractions: undisturbed soil samples, macroaggregates and microaggregates. Based on two methods of sludge application and monitoring over 1 full year, results showed that sludge direct application provides a poorer integration into soil as compared to when sludge was previously mixed with soil and then left on the land. In both cases, 1 year after sludge application, a great part of sludge was integrated well into soil. The proportion of sludge detected within the aggregates was lower than for the undisturbed soil samples, the microaggregates being the poorest in sludge content.